1. Field of the Invention
This invention relates to magnetic recording mediums such as, for example, magnetic tapes, floppy disks, hard disks and allied articles.
2. Description of the Prior Art
In order to improve a wear resistance of magnetic recording mediums, it is the usual practice to add nonmagnetic oxide powders having high hardness such as, for example, aluminum oxide or chromium oxide powder, to a magnetic layer of the medium. However, when such a nonmagnetic oxide powder is added to a magnetic paint, applied onto a nonmagnetic substrate and dried, the resulting magnetic layer has relatively poor surface properties, so that electromagnetic conversion characteristics become poor and particularly, noises will be produced when the medium is reproduced. Presumably, this is because the oxide powder having high surface activity undergoes a reaction with a binder contained in the paint. In an extreme case, the magnetic paint comprising the oxide powder may be gelled during preparation thereof depending on the type of binder. This disenables the magnetic paint to be coated on a base.
In order to overcome the above problem, there has been proposed in Japanese Laid-open Patent Application No. 59-154646 a magnetic recording medium in which a specific type of abrasive powder is treated. More particularly, an abrasive powder such as an aluminum oxide, chromium oxide or titanium oxide powder, is treated on the surface thereof with a compound having one isocyanate group in the molecule thereof. This surface-treated powder is added to a magnetic paint. The surface treatment with one isocyanate group-bearing compound can improve the surface properties of the magnetic layer and can prevent gelation of the magnetic paint as will be experienced in prior art cases. However, the recording medium using an oxide powder which has a compound with one isocyanate group in the molecule thereof coated on the surface thereof, is disadvantageous in that the magnetic head brought in contact with the medium becomes contaminated considerably within a short time of the contact.